This application is based upon and claims the benefits of priority from the prior Japanese Patent Application No. 2001-018901, filed on Jan. 26, 2001, the entire contents of which are incorporated herein by reference.
1. Field of the Invention
The present invention relates generally to a semiconductor laser diode and an optical communication system.
2. Related Background Art
Various light elements such as light emitting elements, photodetectors and light modulating elements are used in an extensive field and placed as basic devices that support an information technology society. Among those light elements, the semiconductor lasers exhibit a narrow spectrum of light emissions, are coherent and can focus light energy of an extremely high density on a small area. Thus, the semiconductor lasers have found applications in various fields such as optical communication, medical care, display devices reading/writing from/to optical discs, etc.
In the above semiconductor lasers, many edge emitting lasers that emit laser beams parallel to substrates thereof are used. Surface emitting lasers that emit laser beams vertical to the substrates thereof are also used. Since the surface emitting lasers involve surface emissions, they are suitable for being constituted as two-dimensional arrays and also for coupling to optical fibers.
Vertical cavity surface emitting lasers (VCSELs) that have laser cavities extending vertical to the substrates thereof have a merit that they operate at a low threshold current, and they have been greatly studied recently. The VCSELs, however, have a drawback that they exhibit no excellent high-temperature characteristic and provide a low optical output although they operate at a low threshold current.
According to embodiments of the present invention, there is provided a surface emitting laser comprising:
a surface emitting laser comprising:
a substrate;
a vertical cavity of layers formed on said substrate for propagating and resonating light along an axis vertical to a surface of said substrate, said light emitted from an active layer by current injection; and
a reflective film disposed concentrically with the vertical axis around the outer periphery of said vertical cavity for reflecting the light from said active layer in a horizontal direction parallel to the surface of said substrate,
the light emitted from said active layer forming a laser beam due to resonation, which laser beam is then emitted in a vertical direction.
According to embodiments of the present invention, there is provided an optical communication system comprising: An optical communication system comprising:
a surface emitting laser comprising: a substrate; a vertical cavity of layers formed on said substrate for propagating and resonating light along an axis vertical to a surface of said substrate, said light emitted from an active layer by current injection; and a reflective film disposed concentrically with the vertical axis around the outer periphery of said vertical cavity for reflecting the light from said active layer in a horizontal direction parallel to the surface of said substrate, the light emitted from said active layer forming a laser beam due to resonation and being emitted in a vertical direction;
an optical fiber for transmitting the laser beam from said surface emitting laser therethrough; and
a photodetector for receiving the laser beam from said optical fiber and for converting the laser beam to an electrical current.
According to embodiments of the present invention, there is further provided a surface emitting laser comprising:
a substrate;
a first DBR formed on said substrate and taking the form of a cylinder having a central axis vertical to a surface of said substrate and exhibiting a high reflectivity to light having a wavelength of xcex;
a first conductive type cladding layer formed on an overall surface of said first DBR;
an active layer formed on an overall surface of said first conductive type cladding layer for emitting light having a wavelength of xcex by current injection;
a second conductive type cladding layer formed on an overall surface of said active layer;
a second DBR taking the form of a cylinder formed on said second conductive type cladding layer and smaller in radius than said first DBR, said second DBR having the same central axis as said second conductive type cladding layer, said second DBR exhibiting a high reflectivity to the light having a wavelength of xcex;
said first DBR, said first conductive type cladding layer, said active layer, said second conductive type cladding layer, and said second DBR composing a vertical cavity;
a burying layer of a second conductive type formed on said second conductive type cladding layer around the outer periphery of said second DBR, said burying layer exhibiting a lower refractive index than said second DBR;
a reflective film covering the outer peripheries of said first DBR, said first conductive type cladding layer, said active layer, said second conductive type cladding layer, and said burying layer, said reflective film exhibiting a high reflectivity to the light having a wavelength of xcex;
the light from said active layer are resonated in a horizontal direction due to reflection of the light by said reflective film and focused in the vicinity of said central axis, the focused light are also resonated in a vertical direction by said vertical cavity to thereby form a laser beam, which is then extractable in the vertical direction from said second DBR.
According to embodiments of the present invention, there is further provided a surface emitting laser comprising:
a substrate;
a cylindrical vertical cavity waveguide formed on said substrate and having a central axis vertical to said substrate, said waveguide comprising a lamination of alternate layers of different refractive indexes for causing light having a wavelength of xcex to resonate in a vertical direction;
a cladding layer formed around the outer periphery of said vertical cavity waveguide on said substrate, said cladding layer exhibiting a smaller refractive index than an average refractive index of said vertical cavity waveguide;
a conductive area formed around the outer periphery of said cladding layer on said substrate, said conductive area comprising a first conductive type cladding layer, an active layer formed on said first conductive type cladding layer for emitting light having a wavelength of xcex by current injection, and a second conductive type cladding layer formed on said active layer;
a reflective film covering the outer periphery of said conductive area and exhibiting a high reflectivity to the light having a wavelength of xcex;
the light from said active layer are resonated in a horizontal direction and also in a vertical direction by said vertical cavity to thereby form a laser beam, which is then extractable in the vertical direction from said vertical cavity waveguide.